BBS is an acronym for Bulletin Board System, which were old timey computer networks. Each was privately owned, and you would dial in to connect. Once there you could share text files/warez/pics, or talk about random stuff with other people. The first one went up in 1978, and they reached their peak in 1996 with over 5000 systems in the USA alone. They were essentially killed off by the Internet. Today, there's about 75 free dial-up BBS's left in the USA. There are hundreds of Telnet-only ones, however they have a tendency to suck.